This invention relates to healing wounds.
Growth factors are polypeptide hormones which stimulate a defined population of target cells. Examples of growth factors include platelet-derived growth factor (PDGF), insulin-like growth factor (IGF-I), transforming growth factor beta (TGF-.beta.), transforming growth factor alpha (TGF-.alpha.), epidermal growth factor (EGF), and fibroblast growth factor (FGF), and interleukin-1 (IL-1). PDGF is a cationic, heat-stable protein found in the granules of circulating platelets which is known to stimulate in vitro protein synthesis and collagen production by fibroblasts. It is also known to act as an in vitro mitogen and chemotactic agent for fibroblasts, and smooth muscle cells.
It has been proposed to use PDGF to promote in vivo wound healing. For example, Grotendorst (1984) J. Trauma 24:549-52 describes adding PDGF to Hunt-Schilling wire mesh chambers impregnated with a collagen gel and implanted in the backs of rats; PDGF was found to increase the amount of new collagen synthesized. However, Leitzel et al. (1985) J. Dermatol. Surg. Oncol. 11:617-22 were unable to accelerate normal wound healing in hamsters using PDGF alone or in combination with FGF and EGF.
Michaeli, et al. (1984) In Soft and Hard Tissue Repair (Hunt, T. K. et al., Eds), Praeger Publishers, New York, pp. 380-394, report that application of a partially purified preparation of PDGF obtained from platelet-rich plasma stimulated angiogenesis when implanted in rabbit corneas. Because PDGF is not an angiogenic growth factor the investigators suggested that an unknown factor in their partially purified PDGF preparation was responsible for the angiogenic effect. Lynch et al , Role of Platelet-Derived Growth Factor in Wound Healing: Synergistic Effects with Other Growth Factors, Proc. Natl. Acad. Sci. U.S.A., Vol. 84, 7696-7700, and Growth Factors in Wound Healing (1989), J. Clin. Invest., Vol. 84, 640-646 demonstrated that purified PDGF preparations, including recombinant PDGF 2 preparations, did not produce a significant effect on connective tissue and epithelial layer regeneration in wound healing studies. In contrast, when purified PDGF was combined with either IGF-I, IGF-II or TGF-alpha a dramatic synergistic effect was seen both in connective tissue regeneration and re epithelialization. Application of IGF-I or II or TGF-alpha alone did not produce any significant effect in connective tissue and epithelial layer regeneration.
Interleukin-1 is a growth factor (or cytokine) which is produced naturally by several cell types, including lymphocytes and macrophages (Kaplan et al , Interleukin-1 and the Response to Injury, (1989) Immunol. Res., Vol. 8, 118-129 . Purified, biologically active IL 1 has a molecular weight of about 17.5 Kd. It occurs in two forms (alpha and beta) with identical biological activity but significant differences in amino acid sequences. Here, the term "IL-1" includes both IL 1 alpha and IL 1 beta, as well as the larger precursor forms of both isoforms. IL-1 is characteristic for both neutrophils and mononuclear cells and stimulates fibroblast and keratinocyte proliferation in vitro, in tissue culture (Kaplan et al.). It is also chemoattractant for epidermal cells in vitro, in culture (Martinet et al., Identification and Characterization of Chemoattractants for Epidermal Cells, J. Invest. Dermatol., Vol. 90, 122-126, 1988) and induces changes in extracellular glycosaminoglycan composition (Bronson et al., Interleukin-1 Induced Changes in Glycosaminoglycan Composition of Cutaneous Scar-Derived Fibroblasts in Culture, Collagen Rel. Res., Vol 8, 1988, 199-208).